Means for obtaining a sensing signal for a servo-controlled color television viewing tube



Jan. 8,- 1957 N. FROMM 2,777,087

CONTROLLED K. MEANS FOR OBTAINING A SENSING .SIGNAL FOR A SERVO- COLORTELEVISION VIEWING TUBE Filed Jan. 22, 1952 "Ill Hill Sensing' Signal so6 Fug. 2. 1e

Signal Input I V Transparent Red l2 Blue Green 26 Sensing Signal l MTronsporenl- Conducting Strip lNVENTOR Kenneth N. Fromm.

United States Patent f) Kenneth N FrommyFortWaynmlni, .assignor toWestinghouse Electric GorporatiomEast.Pittsburgh, Pa, a corporation ofPnnsylvania Application JanuaryaZZ; L195Z',-Seria1 No.:267,60&:

3 Claimsn ((1315-12) My invention relates'to-television tubes and; moreparticularly, to means for obtaining a sensing signal fromraphosphorscreen of a television tube;

Iris-an object of my invention to provide an-improved color'television'tube andci rcui t therefor.

Anotherobiect of my 'invention-is-to' provide-a cathode ray tube andcircuit producing; a reliablesensing signal;

Still another'object of my-invention'isto provide a cathode: ray tubehaving'a' plurality ofstripsof-phosphor material'near an end thereof andhaving means for pro ducing a change. inisecondary electron emissionwhen the cathode ray 'leaves the desired path.v

Still anotherobject' of my'invention is to provide, a color televisiontube having a plurality of phosphor strips whereby the secondaryemission from any group ofstrips isdifferentfrom thesecondary emissionof the strips immediately adjacenttheretoh An ancillary. object of myinvention is to provide means for registering the secondary emissionproduced inthe regionbf saidphosphor strip.

Thenovel features which I consider characteristic of my. invention areset forthwith more particularity in the appended claims. The invention,however, with respect to both the organization and the operationthereof; together with other objects and advantages. may. be bestunderstood'from the following description of specific embodiments whenread in connection withthe accompanying drawing, in which:

Figure 1' is a schematic showing of an apparatusbuilt in accordance withone. embodiment of my invention wherein the tubeanode serves as thesecondary emission collector;

. Fig. 2" is a schematic showing of an apparatus built. in accordancewith another embodiment of. my invention wherein a secondary emissioncollector electrode is pro.-

vided'which is separated from the anode;.and.

ated envelope 4 havingan end plate 6 of transparent materiall This end'plate 6 comprises the picture area of the tube. At the opposite; end of;the tube 4 from the end plate6, an electron gun 8 is provided forproducing a stream of electrons; The-electron gun is a device well knownin the art andwill'notbedescribed in detail here. Between-the electrongun 8- and the end plate: 6; there is l'ocated inside" the tubeenvelope4an anode 10': Betweenthe electron gunfi and the anode 10 in accordancewith principles well known inthe art, deflection electrodes12'are-placcd so-as-toeffect; in accordance with asignal, ahorizontal'or vertical acceleration inthe electronbeam which isproducedbytheclectrongun and accelerated by the fieldbetween'theelectron gun and the anode, By means of thedeflectionelectrodes 12, in accordance with principleswell'known in theart, the electronbeam may; becaused to scan the viewing area. Fastenedto the'inside ofthe-enve1ope4- at the viewing end of the tube 2;isalayer of electrically conducting transparent material 14;whiclrcoverssubstantially all of that' end-of the tube envelope -4.-This electricaly conducting transparent material14 may'beany of severalmaterials which-arewell known in the art; such as'the transparentconducting glass produced by Pittsburgh Plate Glass Company under-thetrade name Nesa; Coated on the inside'of the transparent conductingcoating: 14 are a large number of strips16; 17, 18- ofaphosphormaterial. In the drawing; only a fewsuch-strips are shown, butthesestripsare meant to be indicativeof" the organizationof the muchlarger number'of strips which-would'actually be employed in practice.These strips of phosphor material 16,-17;' and 18am organized inaccordancewithoneembodiment of my invention so 'that-a-fi'rststrip16-comprises a-phosphor material capable of producing-red-lightinresponseto electrons' irnpinging*thereon; such as zincphosphatezMn: A.second phosphorstrip' 17 isprovided adjacent the first phosphorstrip'and is-capable ofproducing-a blue light when electrons impinge thereon.An example of thissecond phosphor wouldbe-zinc sulfidezAg. A thirdphosphor1-strip'18is provided adjacent-the secondphos: phor-stripwhichiscapable of" emitting green light. By way of example, thethirdphosphorrnaterialmight be comprised of zinc orthosilicatezMn; Afourth strip- 19 islocated parallel-to the thirdstrip 18 but separatedasubstantial-distance therefrom so that'a strip of the transparentconducting coating 14- is exposedbetween. the third phosphor strip18 and the fourth phosphorstrip 19; The strip of exposedtransparent-material14 between" the third-strip. 18 and the fourthstrip19; thereforejhas a different coeflicientof secondary emission from thecm efficient of either the-third-strip 18- or the fourth strip 19;

Insome instances, it maybe desirable to employ a mixtureof'a-phosphor-and another material such as AgzO having a high secondaryemission coefficient.

In the embodiment shown in Fig. 1, a, high voltage source of'potential20 is connected between the electron gun 8 and the anode 10; and a lowvoltage source of potential 22' in series with a resistance 24 isconnected between the anode" 10 and the transparentconducting layer 14.An output terminal 26 for the sensing signal is connected through acondenser 28 to the transparent icon.- ducting-layer 14;

In the operation of the apparatus shown, in Fig; 1, electrons producedby the electron gun 8" are accelerated by the anode 10 so as to impingeon the screen comprising the phosphor strips' 16 to 19 and thetransparent conducting layer 14. The electrons which have been formed ina beam of small cross-sectional area bypthe. electron gun 8 aredeflected by the deflection electrodes 12 in accordance with an inputsignal so that the point at which the electron beam impinges on. thescreen is caused to scan the screen. The electron beam is preferablycaused to scan the first phosphor strip 16' first and then scan thesecond phosphor'strip 17;

The path of the scanning beam is preferably sinusoidal as, for example,is shown by the curve 36 in Fig. 3. Let; us assume now that the thirdphosphor strip is being scanned. As the beam scans the third phosphorstrip 18, it may leave its desired course and move over onto the stripof exposed transparent conducting material betweenthe third phosphorstrip 18 and the fourth phosphor strip 19. If thisoccurs, the numberof'secondary electrons emitted per unit time will change.

The secondary electrons emitted by the screen are attracted toward theanode 10 since the anode 10 is more positive than the transparentconducting layer 14. These electrons impinging on the anode 10 cause a.current pulse between thcanode 10 andthe transparent'conducting layer14. When. the scanning beam ceases tov scan the third'phosphor stripls'and starts to scan the strip of exposed transparent material 14,therewill be a change in the number of the secondary electrons impinging onthe anode per unit time because of the difference in secondary emissioncoefficients of the third strip 18. and the transparent material 14.This change in the number of secondary electrons striking theanode 10per unit time causes a change in the current between the anode 10 andthe transparent conducting layer 14. A pulse of current is thus producedwhich changes the output through the condenser 28. Thus, the currentpulses which pass out through the condenser 28 comprise a sensing signalwhich indicates the position of the scanning beam. This sensing signalmay then be employed to correct the potenials applied to the deflectionelectrodes so as to cause the electron beam to change its direction. a

In the embodiment shown in Fig. 2 a separate secondary emissioncollector electrode, 30 is provided for collecting the electronseniitted by the screen in response to electrons impinging thereon. Thesecondary electron collector 30 is connected to the anode 10 through asource of potential 32 and a resistance 34 in series. A change in thenumber of secondary electrons impinging on the collector electrode 30will produce a change in the current across the resistance 34. An outputpulse is therefore produced which varies in response to variations inthe secondary emission.

A system as described herein has a particular advantage-that a very highratio of sensing signal current to noise current may be obtained.For'example letus assumethat the secondary emission coefiicient of thethree phosphors which are separated periodically by a strip of exposedconducting material is so chosen thatthe number of electrons per unittime impinging on the phosphor is equal to the secondary emissionelectrons leaving the phosphors per unit time. Under these conditions,the current through the conducting layer adjacent the phosphors will bezero when the electrons of the scanning beam are impinging on thephosphor. If the secondary emission coefiicient of the exposedconductive strip is any quantity other than one, that is, if either moreor less electrons leave the conductive strip per unit' time than impingethereon, a current will flow between the conductive strip and theelectron gun. Thus, the ratio ofcurrent from the conductive strip tocurrent from the phosphors will be equal to a finite quantity divided byzero. The ratio of the currents is therefore infinite. I a

In accordance with another embodiment of my invention, the fourthphosphor strip 19 may be composed of the same materials as the firstphosphor strip 16. However, the phosphor materials are so chosen thateach strip has a secondary emission coefiicient when bombarded withelectrons, which is susbtantially different from the secondary emissioncoefficients of the strips immediately adjacent thereto; For example,the third phosphor strip 18 is so chosen that a secondary emissioncoefiicient-is substantially different from either the secondaryemission coefiicient of the second phosphorstrip 17 or the secondaryemission coefficient of the exposed area of the transparent conductingmaterial 14located between the third phosphor strip 18 and the fourthphosphor strip 19.

It is understood also that the strip of exposed transparent conductingmaterial 14 could beeliminated and the phosphor strips 16 to 18 sochosen that one of the strips of phosphor, as, for example, the greenstrip 18, has a different coefiicient of secondary emission from the redand blue strips 16, 17. A different pulse would, therefore, be producedwhen the electron beam impinges on the green strip 18 from that producedwhen it impinges on the red or blue strips 16 or 17.

Although I have shown and described specific embodimerits of. myinvention, I am aware that other modifications thereof are possible. Myinvention, therefore, is

second phosphor strip capable of emitting light of .a sec ond wavelength adjacent said first strip, a third phosphor strip capable ofemitting light of a third wave length in response to electrons impingingthereon adjacent said second strip, a fourth phosphor strip capable ofemitting light of said first wave length extending parallel to saidthird phosphor strip .but being separated therefrom by a substantialdistance, output means responsive to the secondary emission of electronsproduced by bombardment of said phosphors and the area between saidthird phosphor and said fourth phosphor with high velocity electrons.

2. In combination, a television .tube having therein near an end thereofa layer of transparent conducting material, a first phosphor strip onsaid layer capable of emitting light of a first frequency, a secondphosphor strip on said layer capable of emitting light of a secondfrequency, a third phosphor strip on said layer capable of emittinglight of a third frequency, a fourth phosphor strip coated on said layerparallel to said third phosphor strip but separated therefrom by asubstantial distance which is capable of emitting light of said firstfrequency, a secondary emission collector ring located inside saidtubenear said layer, means for maintaining saidsecondary collector at ahigher potential than said layer, means for obtaining a signalresponsive to the rate at which said first strip, a third strip ofphosphor material capable of emitting light of a third frequency coatedon said collector electrode adjacent said second strip, a fourth stripof phosphor coated on said collector electrode parallel to said thirdstrip but separated therefrom by a substantial distance and capable ofemitting light of said first frequency, said second phosphor having adifferent secondary emission coeificient from said first phosphor andsaid third phosphor, and all of said phosphors having a differentcoetficient of secondary emission from the coefficient of the regionbetween said third phosphor strip and said fourth phosphor strip, meansfor obtaining a signal from said anode which is responsive to the rateat which secondary electrons impinge thereon.

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